What factors have led to Liverpool's defence seemingly tightening up?

Liverpool's win over Southampton came with their fifth consecutive clean sheet on the road in the league. That last happened in 1985.

At the end of last season, Liverpool manager Brendan Rodgers said he would work on tightening the side up at the back. It may have taken him a while, but the indications suggest he has gone on a long on the face of things.

The system has changed from a back four to a back three and the personnel that seems to be starting the preferred back line looks very different to that from the start of the season.

There are several potential factors this. Simon Mignolet's improvement is one of them, as well as though who sit in front of the back line, while Liverpool try to preserve some of the attacking menace that took them so close to winning their first top flight title since 1990 last season.

But let's have a look at some of the statistics surrounding the defensive unit as a whole. 

Until 16th December 2014:

  Tackles AccuracyErrors lead to shot per gameGoalkeeper punches per gameSaves per gameOutfielder blocks per gameDuels Won per gameAppearances
Liverpool 76% 0.94 0.5 2.56 3 59.44 16

From 20th December 2014

  Tackles AccuracyError lead to shot per gameGoalkeeper punches per gameSaves per gameOutfielder blocks per gameDuels Won per GAMEAppearances
Liverpool 75% 0.1 1.4 2.1 3.2 57.9 10

There are, evidently, a couple of key factors. The tackles accuracy has remained the same, while the duels won per game has dropped. This seems to be an area that Brendan Rodgers wasn't so worried about, as a unit. 

Two eye-catching statistics when it comes to the goalkeeping. On average, Mignolet has had fewer saves to make in the Premier League, but the amount of times the Liverpool goalkeeper has come to punch the ball has almost trebled meaning he has taken on a role that has made him more decisive when it comes to dealing with crosses or set-pieces.

One other statistic to note is the increase in the number of blocks from outfield players in the game. It is probably of little surprise that as the amount of saves the goalkeeper has had to make has declined, the amount of blocks made has risen a little.

It hasn't even been the biggest of changes from Liverpool in terms of statistics. They have clearly found a system that works for the personnel, players like Mamadou Sakho and Emre Can have made a contribution to a more assured back line while Mignolet's brief spell out of the side seems to have done him a lot of good.

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